
Criminal (and some civil) investigations often require a search by law enforcement authorities. Most nations recognize that permitting a search of individuals or property without procedural guardrails can be problematic. In response, they have developed legal principles that balance the inviolability of privacy interests and the need for effective public security. A search warrant is a legal authorization to conduct a search based upon credible information connecting the subject of the search to a crime. Many countries require a judge or magistrate to review law enforcement search requests; others delegate warrant authority to the prosecutor. In some nations warrant requirements are limited to very narrow circumstances or do not exist at all.
This piece provides an overview of search warrant rules adopted by different criminal justice systems.
What is a Search Warrant?
A search warrant is a document signed by a neutral authority permitting law enforcement to search a person or property for evidence of a crime. A warrant requirement may be included in a nation’s constitution, detailed in the criminal procedure law, or made obligatory by virtue of being a signatory to an international human rights instrument. A warrant application must be based on a credible, substantiated belief that a crime was committed (probable cause) and that evidence of illegality will be found. In most countries, the factual basis for a warrant must be truthful and specific, setting forth particularized information about the location to be searched and the evidence to be seized. Warrants must also be timely and executed in a reasonable manner. For example, the warrant may provide a detailed time period for its execution.
Constitutional protections and related code provisions addressing privacy interests and government authority may be general and require judicial analysis and elaboration through court judgments.
History
The Code of Hammurabi, one of the earliest recorded legal codes, does not explicitly mention searches, but it does emphasize fairness and due process, values that underlie the rationale for warrants. The genesis of the modern search warrant has been traced to the American colonial era when residents objected to searches conducted by British officials. Writs of assistance, first used by King Henry VIII in the mid-16th century, gave British officers broad authority to search homes and businesses and seize property. Recognizing this expansive authority was vulnerable to abuse, parliament limited the use of the writs in England, but they were broadly employed by customs officials in the colonies. In 1761, the writ of assistance was challenged in court by Boston attorney James Otis who famously argued “a man’s home is his castle.” This principle was later enshrined in the Fourth Amendment of the United States Constitution, a provision that protects individuals from unreasonable searches and seizures by the government.

Authority to Issue: Prosecutor or Judge?
In some countries, including the United States, searches can only be authorized by a judge. Prosecutors are not considered sufficiently neutral to make the probable cause determination. By contrast, in many other countries, including Germany, although the prosecutor is part of the executive branch, it is deemed to have a quasi-judicial role in the fact-finding process. Prosecutors are considered “organs of justice” and duty-bound to search for and consider inculpatory and exculpatory evidence.
Implementation
The warrant application can be made by submitting a sworn, written affidavit to a judge or prosecutor, in person. Some countries now authorize this process to take place over the phone, video, or electronically.
The scope of a permissible search is typically limited, whether by criminal procedure law or judicial decree. For example, the search of a person is restricted to their immediate area and effects, pockets, and items within their reach such as bags and backpacks. A warrant to search a home or business usually must set forth details specifying the rooms and items (computers, clothes etc.) to be searched. The authority to search electronics (smartphones, computers, servers) may require an additional warrant.

International Standards
Although a search warrant is not mandated by international law, international law instruments and norms affirm the right to privacy. Article 17 of the International Covenant on Civil and Political Rights states: “No one shall be subjected to arbitrary or unlawful interference with his privacy, family, home and correspondence …” The European Convention on Human Rights (Article 8) similarly recognizes an individual’s right to privacy in their home, family life, and correspondence and any governmental interference with this right must be carried out “in accordance with the law and [as] is necessary” to prevent crime and protect the health, rights, and freedoms of others.
Exceptions
Many searches by law enforcement are warrantless, falling into one of the many legal exceptions such as consent, search incident to arrest, and exigency (imminent danger or the destruction of property). Police authorities in most countries may conduct a warrantless search when pursuing a fleeing suspect into a home or building and during administrative inspections of buildings. Most countries that require a search warrant have an automobile exception based on the mobility of vehicles. For example, in Kenya, Singapore, Spain, and the United States, police may search a vehicle if there is probable cause to believe that it contains evidence or contraband; in Canada a vehicle can be searched if there is a risk that the evidence will be moved or lost.
Verification
Some countries enable the subject of a search warrant to petition for verification of the facts used to obtain a warrant. In Poland and Germany, the lawfulness and necessity of a warrant can be contested before trial, whether or not items were seized. By contrast, in the United States, the legality of a search is challenged in pretrial hearings to exclude evidence. In Italy, a defendant can request a judgment for verification only in cases where items were seized. This limitation was criticized by the European Court of Human Rights in a 2018 judgment, Brazzi v. Italy. In that case, the prosecution executed a search during a preliminary criminal investigation with no judicial review before or after the search was executed. The Court ruled that Italy’s law (limiting judicial review to searches where evidence was seized) is contrary to Article 8 § 2 of the Convention and violated Mr. Brazzi’s “right to respect for his home.”

No-Knock Warrants
According to United States Supreme Court precedent, the Fourth Amendment incorporates the common law rule that before entering a building to execute a search warrant, police must knock on the door and announce their identity and purpose. In the 1970’s, law enforcement authorities argued that this notice enabled the destruction of evidence, flight, and posed a danger to officers; a remedy was implemented: quick-knock (knock and wait 15-20 seconds before entry) and no-knock warrants. In the 1980’s and 90’s, their use became more widespread as part of the ‘war on drugs.’ Although the Supreme Court approved no-knock warrants in a 1997 case, it held that judges must examine the facts of each case to assess whether their use was justified. There must be a reasonable suspicion that “knocking and announcing their presence, under the particular circumstances, would be dangerous or futile, or that it would inhibit the effective investigation of the crime.”
Critics of no-knock warrants in the United States argue that they are requested and issued with increasing frequency and often result in greater risk of injury to both suspects and law enforcement officers. Well publicized cases of no-knock warrants resulting in police injuring innocent people led to campaigns to eliminate their use. Twenty-nine states and 21 cities have limited the application of no-knock warrants, and four states have banned them entirely.
In Canada, police, not the courts, have the authority to determine when a no-knock entry is permissible. A judicially approved warrant is not required.

Geofence Warrants
The geofence warrant has been called a ‘reverse warrant.’ Rather than a request to search a particular place or person suspected of a crime, a geofence warrant seeks to identify suspects when none are known, gathering information that may be relevant to an investigation. A geofence warrant does not require the use of detailed information or a finding of probable cause. It is used by law enforcement to compel technology companies to gather information about who was within a particular area (a geofence) during a specified time period. This information – the individual’s location history – is culled from the interaction of a user’s device with GPS, Bluetooth beacons, cell towers, and Wi-Fi networks.
Only United States law enforcement currently uses geofence warrants and their legality has been challenged throughout the country. In December 2023, Google announced that location data will only be accessible from a user’s device and will not be stored in the cloud.
Country Examples











